The UK charges taxes at all different levels of industry. This causes imported products to be more expensive. Happens to the products in the USA too, but the overall tax rate is lower.
Plus in the UK taxes (VAT) is included in the headline price, whereas in the US taxes are shown during checkout (although, yes, US tax is typically around 5%, as opposed to the UK's 20%).
I did a quick calculation and it seems like the UK is "only" being overcharged by $21/£15 when you take into account VAT. Which may exist due to exchange rate shifting and the additional regulatory costs perhaps.
PS - An extra 15% sales tax for free healthcare is a good trade if you ask me. But each to their own. :)
